1. Field of the Invention
The present invention relates to a radio communication apparatus such as a mobile telephone and a portable telephone including a battery as a power supply thereof.
2. Description of the Related Art
In a radio communication system including a base station and terminals, control information such as information for controlling a call may be transmitted through a control channel and speech maybe transmitted through a speech channel. When there is an incoming call from the base station, information for call initiation for calling a specific terminal is generally transmitted through the control channel. The terminal detects the information for call initiation and exchanges necessary information with the base station. Then, the terminal starts speech by means of the speech channel. The terminal is required to monitor the control channel in order to detect the call initiation; the terminal does not always monitor for an incoming call, but monitors for an incoming call for a particular time at regular intervals. The state of monitoring for a request for call initiation is named a state of waiting for a call. Thus, in this state, the terminal operates a receiving circuit only when the terminal performs the monitoring and during other periods the terminal is required to operate a timer function for counting the time until the next monitoring at the minimum.
FIG. 1 is a block diagram schematically illustrating a control channel transmitting unit of a base station and a control channel receiving unit of a terminal in the prior art. In the base station 51, an incoming call control portion 53 detects an incoming call from a network. An incoming call message generating portion 54 generates an incoming call message for the incoming call terminal. An other message generating portion 55 generates messages of various kinds of control information indicative of states and the like of the system which are not directly related to the incoming call. A message constructing portion 56 constructs messages from the incoming call message generating portion 54 and the other message generating portion 55 to form one message block. A transmitting portion 57 transmits the message block constructed by the message constructing portion 56 in synchronism with a slot timing through radio.
In a terminal 52, which is a mobile station, a receiving portion 58 monitors a slot assigned to the terminal 52 and receives a radio wave signal from the base station 51. An incoming call message detecting portion 59 takes out the incoming call message from the received slot. An operation/stop control portion 60 controls to operate and stop each portion of the terminal
Operation of the above prior art will now be described Control data transmitted from the base station 51 is described with reference to FIG. 2. In FIG. 2, a carrier 61 used as the control channel on a radio circuit is divided into slots each having a milliseconds as a unit. A control message 62 provided on the control channel includes a series of various kinds of control information containing incoming call information sent from the base station 51 and is formed as one message block. The terminal 52 monitors the control channel for each slot assigned thereto in the state of waiting for a call and previously arranges together with the base station 51 to monitor the control channel every k slots. In FIG. 2, for example, when the terminal 52 monitors the control channel at slot (n), the next monitoring by the terminal 52 is performed at slot (n+k). Further, when the base station 51 attempts to connect a call to a terminal, the base station 51 provides the incoming call message in any position within a slot to be monitored by the terminal 52, so that the terminal 52 can detect the request for call initiation. For example, when the incoming call information is provided in the message (3) of the slot (n), the terminal 52 can receive the message (3) including the incoming call information for x milliseconds after an elapse of y milliseconds from starting of monitoring the slot (n).
Referring now to FIGS. 3 and 4, operation of the base station 51 and the terminal 52 will be described. As shown in FIG. 3, in the base station 51, when the incoming call control portion 53 detects an incoming call from a line wire (step 71), the control portion 53 requests the incoming call message generating portion 54 to issue an incoming call message (step 72). The call incoming message generating portion 54 issues the incoming call message in response to the request. The message constructing portion 56 constructs the incoming call message and inserts the message into a specific slot (step 73). The transmitting portion 57 transmits the constructed message through radio (step 74).
On the other hand, in the terminal 52, as shown in FIG. 4, the operation/stop control portion 60 operates the receiving portion 58 and the incoming call message detecting portion 59 just before a slot to be monitored by its own terminal is reached and moves from the state of waiting for a call to an operational state (step 81). The receiving portion 58 receives the slot assigned to its own terminal (step 82) and the incoming call message detecting portion 59 examines whether an incoming call message to its own terminal is contained in the received slot or not (step 83). If an incoming call message to its own terminal is present, the operation/stop control portion 60 sends a signal to an incoming call processing control portion (not shown) to perform the call initiation process. If an incoming call message to its own terminal is not present, the slot is continuously received until the slot is finished (step 84). When the slot is finished, the operation/stop control portion 60 stops operation of the receiving portion 58 and incoming call detecting portion 59 and moves from the operational state to the state of waiting for a call (step 85).
In the conventional radio communication apparatus, however, there is the following problem: Whether an incoming call message to its own terminal is contained to the received slot is not understood unless the slot is received to the end thereof and the message is decoded, and the longer the slot time is, the more a battery in the terminal is consumed.
Generally, in a terminal such as the portable telephone which is operated by a battery, how long the time of waiting for a call can be extended in one charging is a very important subject and the electric power consumed to monitor the slot every time so as to detect an incoming call to the terminal cannot be neglected.